The present invention relates generally to door locks and more particularly to locking devices which allow selective limited opening of a door.
Previous devices have principally been limited to bolt and chain locks of the type documented in U.S. Pat. No. 1,479,709 and commonly seen in the market, whereby a bolt reciprocates within a barrel to selectively lock a door in its closed position. When the bolt is disengaged, a selectively detachable chain remains to hold the door from opening beyond a limited amount. While this system has been in use for years, the chain mechanism has generally proven to be breakable by intruders. Consequently, a sturdier system has been required but to date had not been developed.